1. Field of the Invention
The present invention relates to trimming circuits. The present invention also relates to methods for driving the trimming circuits.
2. Description of the Related Art
In a step of manufacturing an integrated circuit which needs a precise voltage level and a precise current value (e.g., an AD converter or a DA converter), it is necessary to employ a method for compensating for variations in characteristics that cannot be reduced by adjustment of manufacturing conditions.
Further, in a step of manufacturing an integrated circuit which needs high yield (e.g., a high capacity storage device), it is necessary to employ a method for switching a connection to a built-in redundant circuit.
A circuit called a trimming circuit is used for such applications. A trimming circuit determines whether an element or a circuit connected in parallel to the trimming circuit is made to be available or unavailable. The state where the element or the circuit connected in parallel to the trimming circuit is unavailable is referred to as a trimming state. For example, a fuse, a zener zap diode, or the like is used as a conventional trimming circuit.
A transistor including an oxide semiconductor in a channel formation region has been known (Patent Document 1). Since an oxide semiconductor layer can be comparatively easily formed by sputtering or the like, the transistor including an oxide semiconductor in a channel formation region can be easily formed.